The present invention relates to a vehicle windowpane antenna apparatus which is mounted on a window of a vehicle such as an automobile.
There is an automobile windowpane antenna apparatus as the most typical one of prior art vehicle windowpane antenna apparatuses. This type of antenna apparatus includes a thin, narrow, strip conductor mounted on a window (usually a rear window) of an automobile, which is employed as an antenna.
In recent automobiles, a defogger is provided almost all over the rear window to serve as a heater for defogging the window. The antenna therefore has to be mounted in a limited space between the defogger and the window frame.
The above prior art automobile windowpane antenna apparatus has the problem that its reception sensitivity cannot be obtained sufficiently in the AM or FM band since a space for mounting the antenna is limited. The apparatus also has the problem that an adjustment for the shape and arrangement of the antenna makes tuning for optimizing the reception performance difficult and a long period of time is required for performing the tuning operation.
In order to resolve the above problems, the present inventors have developed the following vehicle windowpane antenna apparatus and filed it as Japanese Patent Application No. 10-282870 (its corresponding U.S. and EPC applications have been filed). The antenna apparatus comprises a defogger mounted on a vehicle window, for defogging the window, a means for causing the defogger to serve as a slot antenna, and a driven antenna arranged close and opposite to the defogger with a given gap therebetween in such a manner that one side of the driven antenna is mutually coupled to one side of the defogger.
The foregoing vehicle windowpane antenna apparatus has the advantages that its reception sensitivity is high across a wide band and its tuning operation is easy to perform. However, it has the following problem to be solved. When the antenna apparatus is mounted on a rear window of an automobile, it is unclear how to set the dimensions of respective antenna sections and how to arrange these sections in order to obtain the optimum antenna characteristics. It is thus likely that a required antenna characteristic will not be obtained reliably according to the circumstances.